giggity giggity

hi all,just after abit of advice plz, ive got a mondeo tdci 2.0 130ps, when i hard accelerate the engine seems to drop power and the glow plug light flashes, it still drives but seems a bit sluggish. when i stop and turn engine off and turn it back on it drives as it should until i hard accelerate again. it dosent smoke out the exhaust when it does this either. im wondering if this could be the egr valve,if so do i clean it or replace it, thanks for any help.